Flash device and method



June 7, 1960 'H. EVEDGERTON 2,939,984

FLASH DEVICE AND METHOD Filed Nbv. 21, 1957 TRIGGER C/PCU/ 7' INVEN TOR. 951210121 E flQez-tan BY -Z.

AT 702N516 FLASH DEVICE AND METHOD Harold E. Edgerton, Belmont, Mass, assignor to Edgerton, Germeshausen & Grier, Inc., Boston, Mass, a corporahon of Massachusetts Filed Nov. 21, 1957, Ser. No. 697,846

10 Claims. (Cl. 313-484) The present invention relates to flash devices and methods and, more particularly, to flashtubes of the type used for such purposes as flash-photography, stroboscopio illumination and the like.

It has been found that flashtubes and similar discharge devices, particularly when employing gaseous media at high pressures and when repetitively flashed, become subject to shock-wave effects that deletereously act upon the electrodes of the tube or similar device. The expanding gas-pressure shock wave in the tube, resulting from the production of a confined flash discharge between the tube electrodes, has been observed to blast macrascopic pieces from the electrodes; and, in those cases where the electrodes have become elevated in temperature by the hot gas or otherwise, to break up the electrode surface at the free ends of the electrodes and drive or strip particles thereof back along the sides of the electrodes in streams. This effect, of course, is to be distinguished from mere electrode sputtering caused by charged particles, such as electrons or ions, bombarding the electrode surfaces and dislodging microscopic particles thereof. Electrode arrangements designed to be resistant to such sputtering, indeed, may still be subject to the undesirable shoclowave stripping effects above described.

An object of the present invention, accordingly, is to provide a new and improved flash device and method of operating the same that shall overcome the shock-Wave stripping effects and increase the life of such devices. In summary, this end is achieved by displacing the electrodes from the path of the shock-wave blast produced by the gas-discharge between the electrodes. Preferred constructional details are later set forth.

A further object is to provide a novel discharge device of more general applicability.

Other and further objects will be explained hereinafter and will be more particularly pointed out in connection with the appended claims.

The invention will now be described in connection with the accompanying drawing the single figure of which illustrates the invention in preferred form.

Though the description herein is, for illustrative purposes, directed to the important application of flashillumination tubes, it is to be understood that the described techniques may also be employed with other related devices wherein the novel results of the invention are desired. A flash-tube is accordingly shown having a preferably longitudinally extending tubular gasfilled envelope or housing 1 provided with a pair of spaced branch portions or sections 3 and 5 depending transversely therefrom. The envelope may, for example, be of transparent glass or quartz. Disposed within the branches 3 and 5 are a pair of electrodes 7 and 9, illustrated as of cylindrical form, though any other configuration could also be employed. The electrode 7 is an anode connected to the positive or terminal of a main flash capacitor or capacitors C that becomes or become charged through a charging impedance 11 from an energy source, such as rates Patent a battery B, When a switch S is closed. The other or cathode electrode 9 is connected to the negative or terminal. In this type of circuit, the voltage to which the capacitor or capacitors C is charged, however, is not sufiicient in and of itself to effect a flash discharge in the gaseous medium within the envelope 1 between the anode and cathode electrodes 7 and 9.

An auxiliary or trigger electrode is accordingly employed, such as the external winding 13. The trigger electrode 13 is connected by conductor 17 to one side or terminal of a trigger circuit 15 of any conventional nature, such as, for example, of the mechanical-switch, thyratron-switch or electron-tube switch types. The cathode 9 is connected by conductor 19 to the other terminal of the trigger circuit 15 so that, upon application of a trigger impulse from the circuit 15 between the trigger electrode 13 and the cathode 9, the gas within the tube becomes partially ionized, permitting the high voltage stored in the main flash capacitor or capacitors C to become discharged through the envelope 1 between the anode 7 and cathode 9, thereby producing a high intensity brief flash of illumination. Individual flashes for such purposes as flash photography may thus be produced, or repetitive flashes for such purposes as stroboscopy may be produced as described, for example, in my prior United States Letters Patent No. 2,478,901 issued August 16, 1949. The trigger and other circuits of the said Letters Patent may also, of course, be employed in accordance with the present invention.

For some applications, it is preferred that the cathode 9 be of the sintered type described, as an illustration, in Letters Patent No. 2,492,142, issued December 27, 1949 to Kenneth J. Germeshausen. The anode 7, however, since subjected to much higher temperatures in the applications above described, is preferably constituted of tungsten and the like.

In accordance with the invention, the electrodes 7 and 9 are withdrawn a distance D from the lower wall of the longitudinal portion 1 of the envelope, within the branches 3 and 5. The reason for this is that, when the electrodes 7 and 9 are within the longitudinal portion 1, the production of a flash discharge in the gas therein, between the anode 7 and cathode 9, gives rise to an intense pressure shock-wave, schematically illustrated as rightand leftdirected pressure-blast shock wave fronts W. It is these shock waves W that, in sweeping over the electrodes, have been found to produce the earlier-described deletereous electrode erosion or stripping effects. By thus withdrawing all portions of the electrodes within the branches 3 and 5 and out of the longitudinal path of the shock Wave W along the main envelope portion 1, the electrodes have been found admirably well to be spared these undesirable consequences. The depressing of the electrodes to positions external to the shock-wave path, moreover, has been found not to alter the discharge-producing characteristics in the gaseous medium between the anode 7 and cathode 9 provided the distance D is not too great.

In order, furthermore, to relieve the pressure as the shock waves rush to the ends of the tube 1, envelope expansion chambers l and 1" to the right of the branch 5 and to the left of the branch 3, respectively, are provided. Undesirable high pressure points are not thus built up in the intermediate regions of the branches 3 and 5 and the electrodes 7 and 9 therein.

As an illustration, xenon-filled tubes of the above character, operated at pressures of ten or more centimeters, with a tungsten anode 7 and a sintered, cathode 9 depressed a distance D of substantially one eighth of an inch from the bottom edge of a longitudinal tube portion 1, nine inches long and one-half inch in diameter, with expansion chambers 1"and' 1" extending substantially one-half inch to the right and left, respectively, of the branch sections 3 and 5, have been found to be free of the electrode-stripping effects, ,above described when a .100 microfarad capacitor charged to 3000 volts is used.

Als'another example, a quartz flash tube of 6 mm. outside diameter and 4 mm. inside diameter was flashed from 300 watt seconds at 900 volts. about 2 /2 inches with the electrodes 7 and 9 disposed in the side or branch arms 3 and 5 as shown in the drawing. End cavities 1' and 1"of about inch length were provided for the shock-wave expansion. This particular tube Was used as a small-area source by viewing the end-on portion of the straight section of arc. The corners of the electrodes 7 and 9 are'preferably polished smooth since there is a'tendency' of points or projections to melt. a

It is to be understood that while the invention has been illustrated in connection with a straight longitudinal tube 1, other tube configuration can, of course, also be employed as can other types of operating circuits. In all The arc length was an envelope containing a gaseous medium and shaped to provide a main longitudinally extending portion and spaced portions branching-transversely therefrom, a pair of electrodes disposed in the spaced branching'portions but extending only to regions oiiset outside and, external 1 to the main portion so as to be removed from the pressure shock-wave path of a gaseous discharge between the electrodes along the main portion. 7

7. A gaseous-discharge device having, in combination, an envelope containing a gaseous medium and shaped to provide a main longitudinally extending portion and,

spaced portions branching transversely therefrom, a pair of electrodes disposed in the spaced branching portionsbut extending only to regions ofiset outside and external cases, however, the electrodes will be withdrawn from the shock-wave path. Further modifications will also occur to those skilled in the art and all such are considered to fall within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. A gaseous-discharge device having, in combination, an envelope containing a gaseous medium, a pair of electrodes spaced within the medium and between which electric energy may be discharged to produce a flash that gives rise to a pressure shock wave along a predetermined path through the envelope bounded by the wallsthereof, the. electrodes being ofiset outside the'said walls in order to be maintained disposed external to the predetermined path of the pressure shock wave.

2. A gaseous-discharge device having, in combination, an envelope containing a gaseous medium, a pair of electrodes spaced within the medium and between which electric energy may be discharged to producega flash that gives rise to a pressure shock wave along a predetermined path through the envelope bounded by the walls thereof,

the electrodes being ofl'set outside the said walls at points well'inw-ard of the ends of the envelope in order to be maintained disposed externalto the predetermined path of the pressure shock wave at the said points intermediate the length of the predetermined path.

3. A gaseous-discharge device having, in combination,

an envelope containing a gaseous medium, a pair of electrodes spaced within the medium and between which elec- HIE. energy may be discharged to produce a flash that gives rise to a pressure shock wave along a predetermined path through the envelope bounded by the Walls thereof,

the electrodes being oifset outside the said walls in order 1 to be maintained disposed external to the predetermined path of the pressuresshock wave and the said walls of the envelope having expansion chambers along thesaid 4. A gaseous-discharge device having,'in combination, an envelope containing a gaseous medium and shaped to provide a main portion and spaced portions branching,

, to the main portion so as to be removed from the pressure shock-wave path of a gaseous discharge between the electrodes along the main portion, the spaced branching portions being intermediate the length of the main portion to provide expansion chambers for the pressure shock wave at the ends of the main portion.

8. A gaseous-discharge fla'shtube having, incombination, a longitudinally extending tubular envelope containing a gaseous medium and provided with a pair of spaced branch portions extending transversely from the tubular envelope from points intermediate the ends' thereof, a pair of electrodes one disposed in each of the branch portions but extending to regions offset outsideand external to the tubular envelope so as to be removed from the pressure shock-wave path of'a gaseous flash-discharge between the electrodes along the tubular envelope.

'91Agaseous-discharge fiashtube having, in combination, a longitudinally extending tubular envelope con-' vtaining a high-pressure xenon gaseous medium and provided with a pair of spaced branch portions extending transversely from the tubular envelope from points intermediate the ends thereof, a pair of electrodes'constituted of a tungsten anode and a sintered cathode one disposed in each of the branch portions but extending to regions external to the tubular envelope so asto be removed from the pressure shock-wave path of a gaseous flashdischarge between the electrodes along the tubular envelope.

'10. A gaseous-discharge flashtube having, in combination, a; longitudinally extending tubularenvelope conpredetermined path beyond the said offset postion of e V the electrodes. 7

taining a high-pressure gaseous mediumand provided with a pair of spaced branch portions extending .trarisversely from the tubular envelope from points intermediate the ends thereof, a pair of electrodes constituted of an'anode and a sintered'cathode one disposed in each of the branch portions but extending to regionsiexternal tothe tubular envelope so as to be removed from the pressure shock-wave path of a gaseous flash-discharge between the electrodes along the tubular envelope.

References (lited the file of this patent UNITED STATES PATENTS 

